Structural Transformations in Flash Annealed Ultra-Thin HZO Thin Films via Time-Resolved Synchrotron Grazing Incidence X-Ray Diffraction

To extend computational power beyond the era of conventional area scaling of semiconductor circuits, back-end-of-line (BEOL) integration is a promising pathway towards 3D integration of non-volatile memory with logic. This approach increases integration density while reducing latency and energy consumption associated with data transfer. With improved properties over perovskite-structure ferroelectrics, HfO₂-ZrO₂ (HZO) alloys are promising candidates for future nonvolatile memories because of their CMOS compatibility, sub-nanosecond switching speed, and scalability of ferroelectric properties to the nanoscale. However, synthesis of ferroelectric HZO often requires rapid high temperature heating to stabilize the metastable ferroelectric phase, typically employing a rapid thermal annealing (RTA) procedure to heat the entire device stack for processing times of seconds to minutes. In contrast, flash lamp annealing (FLA) quickly heats materials with sub-ms pulses of light that can achieve very low thermal budget during processing which will be beneficial to protect underlying interconnect and dielectric layers while crystallizing higher level materials.
More intense annealing conditions are required to stabilize the polar orthorhombic ferroelectric phase HZO as the film thickness decreases, which is advantageous for decreasing the coercive voltage during device operation. Previous work has demonstrated FLA processing of 10-nm HZO metal-ferroelectric-metal (MFM) capacitors exhibiting similar remanent polarization and coercive field as RTA processed MFM capacitors, but with an imposed thermal budget three orders of magnitude lower than for RTA processing. As such, FLA is a viable candidate for processing ultra-thin HZO MFM capacitors without exceeding the strict thermal budget constraints for BEOL integration.
In this work, time-resolved synchrotron grazing incidence X-ray diffraction (GIXRD) was used for in-situ visualization of phase evolution during FLA processing of MFM stacks at small ferroelectric film thicknesses. Electrical measurements were performed on the MFM capacitors to correlate device performance with phase evolution and optimize processing conditions for integration into memory devices, with the imposed thermal budget of processing calculated using a calibrated computational model. It was found that a FLA with higher energy densities improved crystallization of the HZO thin films, as evidenced from the evolution of the ferroelectric phase during annealing. These differences in the time-resolved x-ray diffraction experiments coincide with improved electrical performance of devices flash annealed at higher energy densities. Furthermore, we will explore the impact of pre-soaking at moderate temperatures with a halogen lamp integrated in the FLA system on the formation of the orthorhombic phase and electrical properties. This study has advanced understanding of phase evolution of HZO thin films during FLA processing in efforts for adoption in BEOL device processing.